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:IQHN W. RADU, 0F NEW YQRK, I31. I11, ASSIGN'OR 'IO WESTERN ELECTRIC GQMIANY,

INCORPORATED, @F NEW YQJRK, It.

Y., A CORPORATION 0B NEW YQJRJK.

-- LEADING-IN CONDUCTOR.

wearer.

Z'J'o Drawing.

' the like.

Platinum and platinum alloys have been used extensively. in the past for leading-in wires in such devices on account of two important properties which such substances have. In the first place, platinum and its alloys with the nobler metals, are not oxidized upon being exposed to the atmosphere, even at high temperatures. Thus when wire composed of such materials is heated preparatory to being sealed in glass, no oxide coat- I mg will form on its surface to prevent a satisfactory tight seal from being made. In the second place, such a wire will possess the same or approximately the same coefficient of expansion as that of the glass employed. This fact will prevent any disruption of the seal when the glass becomes heated during use. While no material has been found which will act in the same manner as platinum in this connection, it is possible to so treat materials such as the bas'er metals, which have not these properties perse, that they may be readily utilized for the abovenamed purpose.

An object of the invention is to so treat wire composed of one or more of the'baser metals that it may be used as a leading-in wire. It is well-knownthat the two salts, sodium borate and sodium meta-phosphate, ossess the property of uniting chemically with metallic oxides under the influence of heat to form new compounds. In fact both of these salts have had wide use as reagents in quali-- tative analysis of the metals, a difierent color being given to the molten salt by the difierent oxides so treated. These salts also have been used as fluxes for sealing wire into glass. In such, a case the wire is dipped into either the moistened salt or its solution, heated for a-moment and then forced into the heated glass. It has been observed, however, that when the sodium meta-phosphate Specification of Letters Patent.

is a

' phate salt, therefore, is due to this superfi- Iatented Aug 22, 1922.

Application filed January 16, 1920. Serial No. 351,977.

salt is employed for sealing Wire into glass a seal, which is similar to that obtained with latinum and the like, is readily secured. pon examination this has been found to be due to a chemical union between the superimposed phosphate salt and the surface skin of the wire. The superiority of the phoscial welding itself.

In carrying out this invention a concentrated afiueous solution of microcosmic salt NaNIL POylI-LO is prepared. The exact of the flux coating to the metal percentage composition of this bath will be governed-by the thickness of the final coating desired. The wire to be coated, such as copper, iron, iron-nickel, etc., is-then passed slowly through the bath and upon. emerging therefrom is covered with a thin film of this solution. It then passes through warm dry air, where the water of solution and of crystallization is entirely driven ofi' and a continuous coating of the anhydrous salt remains. The Wire then enters a chamber which is kept at a much higher temperature, i. e., one which is capableof causing. a gradual fusion of the salt to take place. As this occurs, water of constitution and ammonia are expelled, leaving sodium meta-phosphate NaPO As this compound is formed, it at once reacts with the metallic oxide which is present on the surface of the wire and forms if the wire be made of copper, the compound formed would be NaCulPtL. At this same temperature, however, the salt becomes weld ed to the surface of the wire. No attempt will be made to assign any particular formula to the compound thus produced since it appears rather to be in the nature of a so- "lution of the surface skin of the wire in the flux coating.

' After the above treatment, the wire is slowly cooled and then reeled. The reelsmay then be stored until desired, for use without danger of subsequent cracking ofi of the flux coating. Wire thusprepared, is admirably suited for leading-in wires, inasmuch as the operator-doesnot have to add the flux at the timethe seal is made. There isalso the added advantage that the amount of flux re uired which depends somewhat upon thee emical composition of the glass employed and which may be predetermined, is present in the right proportions and no extraordinary skill in this connection on the part of the operator is necessary. I

While sodium meta-phosphate has been referred to herein, other phosphates which have the properties of fusing and uniting with the oxide and surface skin may be use-d.

What is claimed is: 1. A leading-in conductor comprising a base metal and having a baked-on coating of a phosphate. I 2. A leading-in conductor of a base metal or metals comprising a moisture-frde coating of a phosphate.

3. A leading-in conductor composed of copper, having superimposed thereon a baked-on coating of sodium meta-phosphate. 4; A leading-in conductor of a base metalor metals comprising a baked-on flux coating which is welded to said conductor.

of the metal;

5. A leading-in conductor of a base metal or metals comprising a baked-on flux coating which is chemically united to said conductor.

- JOHN w. RAD-U.- 

